The novel diazabicyclooctane derivative represented by formula (I) below: (2S,5R)—N-(2-aminoethoxy)-7-oxo-6-(sulfooxy)-1,6-diazabicyclo[3.2.1]octane-2-carboxamide (hereinafter referred to as “Compound (I)”) is a β-lactamase inhibitor, and disclosed in WO02013/180197 (Patent Document 1).

A method for obtaining a crystalline lyophilized composition has been disclosed in which a solution of a chemical substance is frozen at a prescribed temperature, and heated to a prescribed temperature, after which the temperature is kept constant (hereafter referred to as a heat treatment step) (Patent Document 2).
Patent Document 3 and Patent Document 4 disclose that an inorganic salt may be added to an solution of a chemical substance in lyophilization methods that involve a heat treatment step.
Patent Document 5 discloses a method for obtaining a crystalline lyophilized composition by subjecting an aqueous solution of a chemical substance containing 2 to 10% (v/v) of a C1-3 alcohol or acetone to a lyophilization procedure that involves a heat treatment step.
Patent Document 6 discloses crystals of compound (I) and production process thereof